Lysozyme thermal denaturation

Refolded Lysozyme Thermal Denaturation. When lysozyme was thermally denatured at pH 5.68 and annealed at lOCPC, precipitation was not observed, but incomplete refolding occurred. For example, a scan of refolded lysozyme after thermal denaturation is shown in Figure 9. In comparison to the native enzyme see Figure 7a), the endotherm is not as sharp and a low temperature shoulder is also evident. We attribute the broadness of the endotherm of the refolded enzyme to disulfide exchange and/or incorrect secondary structure formation. 

Fig. 3. The transition midpoint (rn) of thermal denaturation of a synthetic lysozyme is determined spectrophotometrically by monitoring the decrease in the absorbance at 292 nm with rising temperature. The thermally induced transition for CL is cooperative and obeys the two-state model to a good approximation.52...

The temperature of the thermal denaturation transition increases with decreasing hydration below 0.7 h. 4) The partial specific volumes of several proteins are the same in dilute solution and in the solid at hydration levels above 0.2 h. 5) The circular dlchrolsm spectrum of lysozyme in a film is closely similar to that in solution (30). 

The conformational changes in /J-lactoglobulin during foaming and thermal denaturation were studied by H NMR and 2H exchange spectroscopy.92-93 The properties of three equine whey proteins, alpha-lactoalbumin, /J-lactoglobulin, and lysozyme, have been studied and compared with those of the corresponding bovine milk.94... 

Figure 5 Thermal denaturation curves (upper) and emulsifying properties (bottom) of polymannosyl and oligomannosyl lysozymes constructed by genetic engineering. , wild-type lysozyme O, polymannosyl lysozyme , oligomannosyl lysozyme.

The gross conformation of acetylated lysozyme is similar to that of the native enzyme, as has been shown by measurement of enzymic activity and fluorescence properties.However, protease digestion, t-butyl hypochlorite modification, and thermal denaturation experiments on native, acetylated, and guanidinated lysozymes have demonstrated that acetylation causes a small but significant shift of the (native denatured) transition to the right. It was concluded that the charge balance in the protein plays an important part in maintaining conformation. 

Fig. 1.14 Thermal denaturation of lysozyme in aqueous solution. Differential absorption fs. temperature, [lysozyme] 10 g L pH 1.45, [KCIj 0.2 m. Adapted from Nicolai et al. [40] with permission from John Wiley, Sons, Inc.

The effect of hydration on the thermal denaturation of lysozyme as measured by differential scanning calorimetry has been examined. Tht Raman spectrum of chemically denatured (dimethyl sulphoxide, urea, LiBr, guanidinium chloride, sodium dodecyl sulphate) hen egg-white lysozyme has been studied. ... 

Horsley et al. [29] studied human and hen lysozyme adsorption on hydrophobic, negatively charged, and positively charged sdica. On the average, human lysozyme was found to adsorb in larger amounts than did hen lysozyme. They attributed the difference in adsorptive behavior to the thermal lability of the molecules human lysozyme is more susceptible to thermal denaturation, hence to surface denaturation, than is hen lysozyme. 

Nicoli, D. F., and Benedek, G. B. (1976). Study of thermal denaturation of lysozyme and other glubular proteins by light-scattering spectroscopy, Biopolymers 15, 2421-2437. 

A. E. Mark and W. E. van Gunsteren, Biochemistry, 31,7745 (1992). Simulation of the Thermal Denaturation of Hen Egg White Lysozyme Trapping the Molten Globule State. 

In some cases the products of thermal denaturation are not completely unfolded and retain structured regions. The addition of guanidine hydrochloride often induces another transition. This has been described for ribonuclease, chymotrypsinogen, and lysozyme (Tanford, 1968). 

A AHcai/A/fvH ratio of 1.007 0.011 indicates the validity of the two-state approximation for the thermal denaturation of lysozyme in alcohol-water mixtures (Velicelebi and Sturtevant, 1979). 

Pfeil (1981) concluded that a-lactalbumin is less stable than lysozyme, with a lower thermal transition temperature, lower denaturational enthalpy, lower heat capacity change, and lower Gibbs free-energy change. 

L. N. Bell, M. J. Hageman, and L. M. Muraoka, Thermally induced denaturation of lyophilized bovine somatotropin and lysozyme as impacted by moisture and excipients. J. Pharm. Sci. 84 707-7X2 (1995). 

Figure 8. Effect of the ligand, N-acetylglucosamine, on the thermal unfolding of (a) native and (b) reduced lysozyme. In comparison to the case where the ligand was absent see Figure 7), an increase in denaturation temperature occurs for the native (S C) and reduced (5 0 enzymes when the ligand is present. The increase indicates that the reduced enzyme is able to bind the ligand.

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